Both the manufacturers of appliances and other equipment applications involving high volume unit production, such as furnace fans, blowers for air conditioners, washing machines, dryers, and the like, and manufacturers of motors used in such applications keep trying to reduce the cost of their products. One way to reduce the cost of the motors is to make them lighter, or to make their endshields of material that is, at the time of their manufacture, particularly inexpensive. The cost of materials varies: at one time, aluminum may be the least expensive, while at another, fiber reinforced plastic may be. It is desirable to have an endshield construction that permits use of the least expensive satisfactory material. Single phase induction motors having at least one main winding and a start winding of the resistance start split phase type conventionally have been used in these sorts of applications, because of the economy inherent in their manufacture. While the invention disclosed hereinafter works well with and is described as applied to single phase induction motors, its applicability is not restricted to them.
Conventionally, a single phase induction motor has oppositely disposed endshields mounted on radially flat surfaces of a stator assembly. The stator assembly includes a single phase main winding and a start winding arranged in slots in a laminated iron stator core. A rotor has a shaft journaled in suitably lubricated bearings carried by the endshields. Although the endshields can be attached to the stator assembly in a variety of ways, in the endshield design of this invention illustrated and described, the two endshields have four legs which project into channels or grooves in truncated corners of the stator core. The legs are then secured in place with epoxy injected into the joints between the legs and the walls of the channels. Such constructions are described in U.S. Pat. Nos. 3,343,013 and 4,110,644.
It is known to provide aluminum endshields of a skeleton frame construction rather than a full enclosure, because the motor is located inside an appliance. Present skeleton endshields weigh approximately 1.5 pounds and use 15.7 cubic inches of aluminum in finished form. The structural characteristics of the skeleton design are considered adequate, as established by a long history of successful market application. However, prior attempts to reduce the amount of material in the endshield design has resulted in performance problems. In the past, the cost of aluminum has fluctuated dramatically, and there are and have been a number of attempts made either to reduce the amount of material in the endshields or to find substitute lower cost materials.
Although a completely skeletal endshield of the type illustrated in co-pending application, Ser. No. 08/194,885, accomplishes the objects of reducing the amount of material and providing a structure with a configuration adapted to be used with different materials, there are other considerations that have not been addressed by that application. In some equipment, the skeletal configuration may not have sufficient resistance to deflection. In others, the open construction may not permit the motor to reach an optimum operating temperature, although as is noted in that application, thin webs of material can be employed to reduce the amount of cooling, or, conversely, the air flow pattern may not produce enough controlled flow to cool the windings adequately.
One of the objects of this invention is to provide endshields of a configuration that is adapted to be used in producing endshields of different materials.
Another object is to provide such an endshield which is structurally sound and capable of resisting deflection under severe conditions.
Another object is to provide such an endshield which produces a controlled flow of air over the end turns of the stator winding.
Another object is to provide such an endshield which is economical to produce.
Other objects will become apparent to those skilled in the art in the light of the following description and accompanying drawings.